In many pump systems, the pump must draw liquid through suction from a lower level during normal operation but the pump must first be filled with liquid to create suction sufficient to maintain a steady flow of liquid into the pump inlet. If the pump is shut down and/or otherwise drained of liquid, insufficient suction will be generated once the pump is again in operation to cause self-priming, i.e., to draw the liquid up to the level of the pump by purging air in the pump inlet.
In one particular application, the need for high speed centrifugal pump priming is especially critical. Specifically, fuel pumps utilized in aircraft subjected to a wide variety of manuevers such as the steep banks, climbs, rolls, dives and the like performed by military aircraft can and do loose prime during flight in addition to dry start-up conditions. As a rsult, the impeller of the pump must be wetted so suction can be generated and air in the pump inlet can be purged.
Among the many attempts to provide a self-priming pump system is the one disclosed in Wood U.S. Pat. No. 1,837,697. The self-priming pump disclosed therein has a priming chamber which is formed such that air collects in the upper portion for subsequent discharge and liquid remains in the lower portion for use in priming. Other means of self-priming a centrifugal pump include that disclosed in Porter et al U.S. Pat. No. 3,741,675. The self-priming pump disclosed therein utilizes an automatic air release valve connected to the discharge side of the pump for venting air from the system during the priming cycle. Still other self-priming pump systems are disclosed in U.S. Pat. Nos. 1,461,622; 1,997,418; 2,059,288; 2,391,769; 3,078,806; 3,381,618; 3,726,618; and 4,255,079.
In providing a self-priming pump system for aircraft fuel supply, a problem is to generate and maintain sufficient suction during dry pump start-up to achieve self-priming. It is a related problem to reprime the pump during operation particularly during aircraft manuevers that can cause fuel to drain from the pump and inlet line whereby the inlet line can be filled with air. Moreover, another problem is to achieve self-priming in an aircraft fuel system with a simplified design that reduces weight and cost.
While overcoming problems of this type, it is also important to provide self-priming of sufficient capacity for an aircraft fuel system so that it is capable of quickly purging air from the pump inlet. It is also desirable to provide self-priming operation upon demand, but operational only when needed in order to eliminate the additional power consumption, size and weight of the pump drive or motor after the pump is primed or reprimed and the self-priming function is then not needed. Further, it is desirable to provide a self-priming pump which is efficient so that the self-priming function does not severely reduce the overall efficiency nor so increase the size, weight, or power consumption of the pump. It is further desirable to eliminate the need for a check valve on the pump inlet and to separate, conserve and recirculate the priming liquid to reduce the volume and weight of priming liquid and its reservoir. Still further, it is desirable to provide a self-priming pump where the self-priming apparatus does not compromise the suction capabilities of the pump.
The present invention is directed to overcoming the above stated problems and accomplishing the stated objects.